Factory Remington Model 870 Special Purpose Extra Deer Barrel 20 Gauge 3 Inch Chamber 18.5 Inch Fully Rifled Cantilever With 2-7x32mm Scope. This will not fit the older 20 gauges built on the 12 gauge frame.p Heavy contour fully rifled barrel. Mounted 2-7x32mm shotgun scope. Comes mounted and bore sighted. Rigid cantilever scope mount. Fits Express, Special Purpose and Wingmaster. This will not fit the older 20 gauges built on the 12 gauge frame.